DECATUR, Ga. (AP) — The 20-year-old man who police say went to an Atlanta-area school heavily armed and exchanged gunfire with officers before surrendering was a normal kid growing up, but began to change as a teenager and engage in behavior that was threatening to others, his brother said.

Tim Hill told CNN's Piers Morgan on Thursday that when he and Michael Brandon Hill were growing up, he was "like any other kid," playing outside and in the woods.

But Tim Hill added, "Once he started hitting his teenage years, something happened with him. Everything just started changing after doctors started messing with his medicines here and there, and changing them up and putting him on a different one and institutionalizing him multiple times to correct his medicine. It just escalated from there."

He said Michael Hill set fire to the family's home when eight people were inside sleeping — the fire was discovered before it spread — and at another point their mother awoke to find him standing over her with a butcher's knife.

"My stepfather and mother ended up having to lock up...like all the knives in the trunk of the car, just to protect everybody in the home," Tim Hill told Morgan.

Tim Hill also confirmed that his brother threatened his life on Facebook, prompting him to call police. He said he feared for his life.

The older brother's comments came two days after a school bookkeeper helped persuade Michael Hill to surrender to police following a frightening standoff and shooting Tuesday at Ronald E. McNair Discovery Learning Academy in Decatur, a suburb east of Atlanta.

Police and school officials said that school bookkeeper Antoinette Tuff helped avert a tragedy after she was taken captive by Hill. He went to the school armed with an AK 47-style rifle and nearly 500 rounds of ammunition, police said.

Lines of young students raced out of the building with police and teachers escorting them to safety, recalling the chaotic scene last December outside a Connecticut elementary school, where a gunman killed 20 students and six educators.

On a recording of a 911 call released Wednesday, Tuff can be heard relaying messages from Hill to DeKalb County emergency dispatcher Kendra McCray before convincing the gunman to surrender. She tells the dispatcher that Hill said he wasn't there to hurt the children but wanted to talk to an unarmed officer.

"He said, 'Call the probation office in DeKalb County and let them know what's going on,'" Tuff is heard telling the dispatcher. "He said he should have just went to the mental hospital instead of doing this, because he's not on his medication."

No one was injured, but police said the suspect shot into the floor and exchanged gunfire with officers who had surrounded the school, which has 870 students in pre-kindergarten through fifth grade. With bullets flying, Tuff urged him to come back inside and give up.

"I knew (police) were gonna kill him. And I knew he was not in his right state of mind," she told CNN's Anderson Cooper on Thursday night.

On the program, she had a tearful on-air reunion with McCray, the dispatcher who stayed on the phone with her as she reassured Hill that surrendering peacefully was the right thing to do. Tuff also received a call in the network's makeup room from President Barack Obama. She said Obama wanted her to know how proud he was of her.

"You can't get any better when you have a great leader in front of you," a beaming Tuff is shown telling the president.

Time and again, Tuff stressed that her faith got her through the episode.

"That was nobody but God's grace and mercy, because I can truly tell you I was terrified inside," she said.

She said she was praying the entire time she talked with Hill, asking God what she should say.

McCray said she was frightened, too, particularly when Tuff began telling her Hill was getting agitated.

"I had to put my phone on mute (and say), 'Hey, he's getting agitated. We have got to move.'"

Tuff is "a true hero," McCray said on the program. "You did so great. I've never had a caller where the caller was so calm and so confident in what they were saying and so personable. You made my job a whole lot easier."

Hill is charged with aggravated assault on a police officer, terroristic threats and possession of a firearm by a convicted felon. Police declined to discuss what he told them when questioned.

Police on Wednesday released an undated photo of Hill posing with an assault rifle that they believe is the one used at the school.

Authorities said Hill got the gun from an acquaintance, but it's not clear if he stole it or had permission to take it. His motive is still unclear.

Tim Hill expressed frustration that authorities hadn't done more to deal with his brother's mental condition before Tuesday. He said he doesn't believe his brother would have harmed Tuff or the schoolchildren.

"I don't think he was there to do that," Tim Hill said of his brother. "He's always had a problem with the cops."

Tuff told Cooper she'd like to visit Hill and speak with him again.

"He's a hurting soul, and so if there's any kind of way I can help him and allow him to get on the right path — we all go through something," she said during the interview.

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Phillip Lucas reported from Atlanta.

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